1. Technical Field
This invention relates generally to antenna circuits and in particular to an antenna circuit with a fractal ground plane.
2. State of the Art
Global Navigation Satellite Systems are in widespread use to determine the location and/or attitude of a body. A Global Navigation Satellite System (GNSS) includes a network of satellites that broadcast GNSS radio signals. GNSS receivers are able to determine their location by receiving GNSS satellite signals from a number of different GNSS satellites. Examples of GNSS systems include Navstar Global Positioning System (GPS), established by the United States; Globalnaya Navigatsionnay Sputnikovaya Sistema, or Global Orbiting Navigation Satellite System (GLONASS), established by the Russian Federation and similar in concept to GPS; and Galileo, also similar to GPS but created by the European Community and slated for full operational capacity in the near future.
It is necessary for a GNSS receiver to receive GNSS satellite signals from a number of different GNSS satellites in order to compute location or attitude. The GNSS receiver obtains the GNSS satellite signals from a GNSS antenna. The ideal gain pattern for a GNSS antenna has gain only above the horizon (about 5 degrees above and higher) and no gain below the horizon. Achieving this ideal gain pattern would require an infinitely large ground plane electrically coupled to the GNSS antenna. While a ground plane of infinite size is not feasible, increasing the size of the ground plane is desirable. However, increasing the physical size of an antenna's ground plane conflicts with the common requirement of small size for portable products. Thus what is needed is a ground plane for use with a GNSS antenna that appears electrically larger than its physical size.